A current of electrons traversing a landscape of localized spins possessing non-coplanar magnetic order gains a geometrical (Berry) phase which can lead to a Hall voltage independent of the spin-orbit coupling within the material--a geometrical Hall effect. We show that the highly-correlated metal UCu5 possesses an unusually large controllable geometrical Hall effect at T<1.2K due to its frustration-induced magnetic order. The magnitude of the Hall response exceeds 20% of the u=1 quantum Hall effect per atomic layer, which translates into an effective magnetic field of several hundred Tesla acting on the electrons. The existence of such a large geometric Hall response in UCu5 opens a new field of inquiry into the importance of the role of frustration in highly-correlated electron materials.
We show that a single impurity embedded in a cold atom bosonic Mott insulator leads to a novel polaron that exhibits correlated motion with an effective mass and a linear size that nearly diverge at critical value of the on-site impurity-boson interaction strength. Cold atom technology can tune the polarons properties and break up the composite particle into a deconfined impurity-hole and boson particle state at finite, controllable polaron momentum.
